The overall goal of the proposed research is to understand how inner ear mechanisms determine the neural code that relates sounds to nerve messages that enter the brain. Knowledge of these mechanisms is important for several reasons: (1) Determining the bases of the code is an intrinsically interesting scientific problem involving integrated knowledge of mechanical, electrical, biological and chemical processes at organ, cellular, membrane, and molecular levels all focussed on understanding the role of the inner ear in hearing. (2) The results should have significance for sensory reception, in general, for mechanoreception in particular, and especially for understanding the acoustico-lateralis systems which include the lateral-line organs found in fish and amphibia as well as vestibular and auditory organs found in all vertebrates. (3) The practical benefits of this knowledge should also include more precise delineation of inner ear disorders, suggestions for treatment, development of prosthetic devices, and incorporation of knowledge of inner-ear processing into the design of systems for processing speech. The specific objective for the proposed grant period is to understand the mechanical processes in the cochlea that link sound-induced motion of the receptor organ to motion of its constituent structures, including the tectorial membrane, the hair bundles of hair cells, and the individual stereocilia that make up a hair bundle. The material properties (including osmotic, mechanical, and electrical properties) of the tectorial membrane will be measured in both isolated tectorial membrane preparations (in the mouse, chick, and the alligator lizard) and in an in vitro preparation of the alligator lizard cochlea. The relations among the sound-induced motion of the receptor organ, tectorial membrane, hair bundles of hair cells, and individual stereocilia in a hair bundle will be investigated using video microscopy of an in vitro preparation of the alligator lizard cochlea.